1. J. L. Synge,Relativity: The General Theory(North-Holland, Amsterdam, 1964);
2. Relativity, Groups and Topology (Les Houches 1963)(Gordon and Breach Science Publishers, New York, 1964).
3. R. C. Buck,Advanced Calculus(McGraw-Hill, New York, 1956).
4. Singular hypersurfaces and thin shells in general relativity
5. Über die Grenzbedingungen des Schwerefeldes an Unstetigkeitsflächen